Mosquitoes are essential for the transmission of several human diseases, including malaria, yellow fever and viral encephalitis. As part of an integrated approach to infectious disease control, it is important to understand the role of mosquitoes in disease transmission. Recently, the powerful tool of germ-line transformation has been developed for Aedes aegypti mosquitoes. The proposed research will employ ovary-specific vitelline envelope gene promoters to drive the expression of foreign genes in transgenic mosquitoes following a blood meal. The ability of these promoters to drive the expression of foreign genes in the ovary will be tested with the use of a fluorescent reporter gene. It is expected that fluorescence will be detected in the mosquito ovaries following a blood meal. The vitelline envelope genes are regulated by 20-hydroxyecdysone. This transgenic system will also allow for a precise study of the mechanism by which this steroid hormone regulates gene expression in the ovary. Despite intensive control efforts in the Upper Midwestern States, LaCrosse encephalitis virus remains a significant public health problem. The virus is maintained and amplified via the mechanism of transovarial transmission by its mosquito host. In the proposed research, vitelline envelope promoters will be fused to a recombinant single-chain antibody against LaCrosse virus. This construct will be introduced into the mosquito germ line using a Mariner or Hermes transformation vector. This strategy will facilitate the in vivo expression of an anti-LaCrosse protein in mosquito ovaries. The recombinant antibody clone will be constructed by methods that will employ an existing hybridoma cell line that expresses a monoclonal antibody against LaCrosse virus surface glycoprotems. This will be an important part of ongoing research to understand the molecular interactions between mosquitoes and viral pathogens, particularly the role of transovarial transmission of LaCrosse virus through mosquito populations.